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The use of different phosphazene bases has been investigated as catalysts in polymerization of [R,S]-4-benzyloxycarbonyl-3,3-dimethyl-2-oxetanone (dMMLABz) in presence of carboxylic acids used as initiators. Whatever the catalyst considered (P1-t-Bu, P2-t-Bu, or P4-t-Bu) a very good control over the polymerization has been obtained in terms of polyester molecular weights and end-groups fidelity as attested by spectroscopic techniques such as 1H NMR, gel permeation chromatography (GPC) and matrix assisted laser desorption ionization-mass spectrometry (MALDI−MS) experiments. Characterized by a complete absence of transfer reactions, the system allows for the generation of very high molecular weight PdMMLABz trough a mechanism selectively involving the “O-alkyl” scission of the β-lactone monomer. A clear dependence of the basicity of the phosphazene catalyst on the overall polymerization kinetics has been observed where the most basic catalytic species, i.e., 1-tert-butyl-4,4,4-tris(dimethylamino)-2,2-bis[tris(dimethylamino)phosphoranyl-idenamino]-2Λ5,4Λ5-catenadi(phosphazene) (P4-t-Bu), shows the highest active ion-pair. Accordingly, P4-t-Bu allowed for the synthesis of PdMMLABz chains characterized by a number-average molecular weight higher than 1.5 × 106g mol−1. [ABSTRACT FROM AUTHOR]

Aromatic substitution reactions of selected ionized benzenes derivatives (chlorobenzene, nitrobenzene, dimethylphtalates) and phenoxy cation using neutral methyl isocyanide as a nucleophile are shown to efficiently occur in the gas phase. Nitrilium ions are produced in high abundance during these processes. These reactions have been performed in the hexapole collision cell of a large-scale hybrid tandem mass spectrometer. Computed 298 K enthalpy diagrams at the B3LYP/6-31+G(d,p) level of theory confirm the exothermic formation of the N-methylbenzonitrilium ions starting with ionized chloro- and nitrobenzene molecular ions. In this last case, two other exothermic processes are also detected: (i) an oxygen atom transfer yielding ionized nitrosobenzene and neutral methyl isocyanate and (ii) a loss of carbon monoxide from the ion/molecule reaction product generated when metastably generated phenoxy cations (produced in the hexapole collision cell) react with methyl isocyanide. Using extended theoretical calculations, several reaction pathways have been derived. The behavior of the three isomeric dimethyl phthalates has been investigated in the same way. [ABSTRACT FROM AUTHOR]

Polythiophenes with alcohol, tosylate, azide, ethynylene, carboxylic acid, and amine end groups were prepared by a combination of functionalized nickel initiators and postpolymerization reactions. The azide and ethynylene polymers were subsequently used in a click reaction to produce a conjugated block copolymer. Finally, a conjugated triblock-copolymer was synthesized by means of a chain growth polymerization initiated by a binuclear nickel initiator. [ABSTRACT FROM AUTHOR]

The chemistry leading to the competitive eliminations of H, CH3, and OCOCH3from adducts of ionized methyl benzoate and neutral methyl isocyanide has been explored using density functional theory molecular orbital calculations. The energies of the various reactants and transition structures were estimated at the B3LYP/6-31+G(d,p) level of theory. Nucleophilic aromatic substitution is proposed to account for the H and OCOCH3eliminations. The corresponding σ-complex intermediates, B1ipsoand B1ortho, are stable species lying in deep energy wells situated 70 and 120 kJ/mol, respectively, below the reactants, ionized methyl benzoate and methyl isocyanide. The latter complex, B1ortho, may be also at the origin of a multistep rearrangement involving hydrogen migrations and methyl elimination from the original methoxy group of the benzoate moiety. [ABSTRACT FROM AUTHOR]